Electric induction furnace and method of operating the same



Dec. 14, 1937. SUMMEY 2,102,582

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAME OriginalFiled April 14, 1932 8 Sheets-Sheet l [NVENTOR BY /7/'f A TORNEY:

D. L. SUMMEY Dec. 14, 1937.

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAME- 8Sheets-Sheet 2 Original Filed April 14, 1932 BY 5 ATTORNEYS.

MIBMMW9-MWM Dec. 14,-1937. SUMMEY 2,102,582

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAME.

Original Filed April 14, 1932 8 Sheets-Sheet I5 BY M ATTORNEY:

Dec. 14,1937. D SUMMEY 2,102,582

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAMEOriginalFiled April 14, 1932 8 Sheets-Sheet 4 Q Q 7! o e Z a 13 l0 1% if4 E21 [2 INVENTOR Eh mg Jar/u z. raw/w):

I wim 300M, VM1 W t-4 D. L. SUMMEY Dec. 14, 1937.

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAME OriginalFiled April 14, 1932 8 Sheets-Sheet 5 I'NVENTOR ilk/0 fay/72v BY MATIORNEYJ M, Yam T41 0'. L. SUMMEY Dec. 14, 1937.

ELECTRICINDUCTION FURNACE AND METHOD OF OPERATING THE SAME OriginalFiled April l4, 1933 8 Sheets-Sheet 6 a W R 0 my ml 0 '3 2 am I 00d,

Dec. -14, 1937. p. 1.. SUMMEY 7 2,102,582;

ELECTRIC INDUCTION FURNACE AND METHOD OF OPERATING THE SAME originalFiled April 14, 1932 8 Sheets-Sheet 7 .Q R O i\ M w w I 11 4- I 'I QIlih IL" I I Q W" N Q & m

' v m N e@ I) Y X). J! t\ INVENTOR 5 04m 1. Jaw/[x BY M ATTORNEYS Dec.14, 1937. SUMMEY 2,102,582

ELECTRIC INDUCTION FURNACE AND IETHOD 0F OPERATING THE SAMEOriginabiilod April 14, 1932 8 Sheets-Sheet 8 INVENTOR Y 'uw auuyw. m

Patented Dec. 14, 1937 PATENT OFFICE ELECTRIC INDUCTION FURNACE ANDMETHOD OF OPERATING THE SAME David L. Summey, Waterbury, Conn.; TheColonial Trust Company and Richard P. Weeks Summey, deceased, Company,Connecticut executors of said David L. Summey, assignors to SeovillManufacturing Waterbury, Conn., a corporation of Application April 14,1932, Serial No. 695,147 Renewed June 18, 1935- 35 Claims.

This invention relates to metallurgical apparatus, particularly to anelectrical furnace for melting metal or for maintaining it in amoltencondition and to the method of operating the same, and has for an objectthe provision of improvements in this art. The apparatus is applicableto the melting or treatment of various metals .and alloys but inasmuchas the present embodiment has been employed and is illustrated inconjunction with related apparatus for refining copper and other easilyoxidizable metals, it will be described with special reference to suchan employment; but this is done without any intention of limiting thescope of the invention thereby.

In the accompanying drawings which illustrate this embodiment of theinvention;

Fig. 1 is a plan view of the electrical furnace which is the specialsubject of the present application. together with certain relatedapparatus;

Fig.2 is a side elevation of the furnace with one of the heating unitsremoved;

Fig. 3 is an elevation of the pouring end of the furnace taken on theline 3-3 of Fig. 1;

Fig. 4 is an elevation of the charging end of the furnace taken on theline 4-4 of Fig. 1;

Fig. 5 is a vertical axial section taken on the line 5-5 of Fig. 1;

Fig. 6 is a vertical section taken on the line 6-6 of Fig. 1;

Fig. 7 is a transverse vertical section taken on the line of Fig. 1;

Fig. 8 is a section taken on the line 8-8 of Fig. 9 is a compositediagram showing the shape of the metal channel for a heating unit takenat several places indicated in Fig. 7; and

Fig.. 10'is a diagrammatic view of the furnace v in position for-theremoval of a heating unit.

The plant with which the present apparatus has herein been illustratedis shown in full in my co-pending application Serial Number 619,474filed June 27, 1932, Patent Number 2,060,134, November 10, 1936, and isshown in substance in my co-pending application Serial Number 535,829,filed May 8, 1931, Patent Number 2,060,133, November 10, 1936. Thoseparts of the plant which are closely associated with the presentapparatm are shown in Fig. 1 and comprise the hearth B of a two-hearthoscillating furnace, a hood I5 enclosing the space between a mold aboutthe spout 2i (see Fig. 6), and awheel 22 for supporting a plurality ofmolds.

As shown in Fig. 7, the furnace l6 comprises a single horizontalcylindrical hearth or chamber 25 which is oscillatable about its axis Zfor pouring metal or for tilting the furnace for the removal of aheating unit. "Cylindrical here does not necessarily refer to a rightcircular cylinder but is used in its broad sense to refer to a hearthwhich is of substantially uniform cross section throughout its length inthe lower metalholding portions, thereof. The furnace chamber 25 islined with refractory material 26 which is supported by a substantialmetal casing 21. The lining may either be of rammed material or ofshaped firebrick, the latter being employed in the interior for placingthe lining. Openings 30 a which are normally sealed by the caps 3l' andwhich are plugged up. as shown, when not used, permit gases of anydesired kind to be piped into the furnace.

Supporting rails 32 are secured beneath the hearth casing and theserails rest (Figs. 2 and 3) .upon flanged wheels 23 supported upon shaftsI carried by bases 35.

Means are provided for oscillating the furnace. Referring to Figs. 2 and3, an arcuate rack 31 is secured toone end of the casing. Upon one ofthe roller shafts 34 there is rotatably disposed a gear 38 which is inmesh withthe raclrll. A drive pinion 39 is mounted upon a pinion shaft40 in operative relationship with the gear 28. The shaft 40 is providedwith a flexible connection 4|. Referring to Figs. 1 and 2, the shaft 4|is driven through a gear train of the non-backdrive type housed within agear case 42 by a motor M. For normal operations the ,angle -of 44quickly stops the motor when the current is cutoff.

The furnace may be charged with-solid metal which is to be melted or'with molten metal which ,is to be maintained in the molten conditionuntil it is poured. Herein the furnace is shown to be equipped for thelatter scheme of operation, so, as shown in Fig. 5, it is provided withan opening All in the top at one end for receiving molten metal from thespout ll of the melting furnace. While the furnace is shown as a unit ofa plant wherein molten metal is supplied, the furnace itself isconstructed for separate melting. For this purpose it is provided with abafie d6 extending from the -roof down below the normal lowest metalline. This keeps the solid and coldest metal (which is also the mostimpure) near the .charging end and away from the pouring end of thefurnace.

It also retains gaseous elements created during the refining, as forexample, zinc components when melting brasses.

= The plant or system is designed to produce metal of great purity. Inparticular atmospheric oxygen is kept out of the'system. The furnace itand the hearth B of the melting furnace have movement relative. to eachother, so the connecting enclosure is articulated to accommodate thismovement while 'at the same time excluding air. Herein (Fig. 5) the endof the hood i5 is rigidly attached to the furnace it and is providedwith a 'flat vertical end surface which slides along the face of avertical plate G8 which is attached to the hearth .B. The plate isadjustable and spring pressed against the end of the hood and in allpositions remains sealed about the'spout W. This articulated hoodedconnection need not be considered in detail herein since it is fullydescribed in another application.

At the pouring end of the furnace there is likewise relative movementbetween the spout 2| and the mold 20.

strainer i9. The strainer is vertically movable so that it may be seatedupon the upper end of a mold when the latter arrives therebeneath, or

is adjustable and spring pressed against the end' of the hoodand is atall times sealed about the spout 2|. This articulated connection is alsodescribed in detail in another application.

Notonly are the furnace and all of its conneckeeping the metal pure orfor purifying it if it should be contaminated. This may be produced bygas injection or by a suitable covering for the molten metal; Herein acovering of carbon C is Y shown upon the bath P of metal in the furnace.

Carbon is a strong deoxidizing agent and also serves to maintain carbonmonoxidvgas in the furnace chamber under a slight pressure whereby ifthere is any leakage through the articulated connections it will beoutward and not inward. I I

A baflie 50 extends downward toward the spout 2| to retain the coveringwithin the furnace.-

The articulated connection here (Fig. 6) includes the hood i8 and theThe metal beyond this baflie-does not enter fully into the generalcirculation which is maintained within the main bath and is likely tofreeze. If metal freezes here it is difiicult to remove since theenclosing hood makes it inaccessible. So

means are provided for heating the metal here to keep it molten. Thismeans, as shown in Fig. 6, comprises resistors 5! connected in anelectrical circuit by electrodes 52. The resistors and electrodes areplaced above the metal but are subject to injury by splashing metal so athin refractory plate 53 is placed between them and the metal toprotect-them.

An opening 55 (Fig. 5) is provided in the end of the furnace forcharging carbonaceous or other material, for sighting into the furnace,or for attaching a frame carrying a pyrometer for measuring thetemperature in the furnace. This opening is closed by a refractory lineddoor 55. The door is vertically slidable behind guides 5t and may besealed tightly against the furnace by hand screws 5? threaded throughthe guides. The door is supported by chains 58. Referring to Figs. 2 and3, the chains are suspended from pulleys 59 which are fast on a hoistshaft 6%. The shaft is rotatably supported on columns 6! which aresecured to the top of the furnace V casing.- The weight of the door ispartially balanced by counterweights 62 suspended by cables 83 attachedto pulleys 6G fast on the shaft 60. The cables pass forward over idlerpulleys 55 fast on an idler shaft 66 which is supported in bearings uponthe columns. The counterweights are kept in alignment in all tiltedpositions of the furnace by strap guides 57. The shaft Ell is rotated bya worm and gear connection 68, 69 from a shaft ill by a chain it passingaround a notched sheave 62 fast on the shaft.

The door is provided with a removable sight glass mounting l3 foraffording a view into the interior of the furnace.

Means are provided for heating the bath of metal and stirring it intofrequent and intimate contact with the carbon covering. The heatingmeans preferably comprises a plurality of electrical transformer unitsl'i. As shown in Figs. 1 and '2, there are two such units in use and athird position for another unit, which is blanked off by lining materiaPand -a cap l8. If desired more units may be provided and preferably eachunit is supplied with current from one phase of a multi-phase source ofcurrent.

The transformer units require cooling and for this purpose air issupplied by branch conduits 19 leading from a trunk conduit 80 Thebranch conduits are provided with control dampers 82-.

tendsto the end of. the furnace where it is turnably connected at theaxis of oscillation Z of the furnace with a supply conduit 8|. tionssealed but a non-oxidizing or deoxidizing condition is maintained withinthe furnace for' Referring to Figs. 'Land 8, the furnace casing 21 isprovided with a flanged tubular extension,

84 for each heating unit. To'this is bolted the shell 85 of the unit. Itis desirable to electrically insulate the heating transformer shell fromthe furnace casing. This is done in such a way as to avoid theinstallation. of the insulation atthe time when the-unit is attached tothe casing. It will be realized that the units may be replaced while thefurnace is in operation and in such a case the replacement must beeffected so quick-' ly that there is little time forplacing insulation.As seen in Fig. 8, this is accomplished by bolting a plate 86 to theshell by insulated bolts 8l, -with a sheet of insulating material 88placed between the shell-and the plate. This can be done before theunits are brought to the furnace. When attaching the unit to the furnacethe plate 86 is bolted directly to the extension 84 by bolts 89, noelectrical insulation being used.

The heating units are supported upon brackets 90 which are attached tothe furnace shell. The mounting of the unit upon the brackets is alsodesigned for speed of replacement. Plates 9| are secured by electricallyinsulated bolts 92 to the brackets, there being electrical insulatingsheets 93 between the plates and brackets. When attaching 'the heatingunit to the furnace it is placed with its feet 84 upon the plates SI andslid endwise until it connects with the flanged extension 84. The feet94 are then secured to the insulated plates 9! by bolts 95, noelectrical insulation being necessary unless the bolts pass through theplate 9|. Even then no insulation is required between the feet 94 andthe plates 9|,

So that the sliding movement may be quickly effected and without injuryto any insulation.-

The shell 85 of the heating unit, which is preferably of a non-magneticmaterial like bronze, comprises a lower portion 85a, including bottomand sides, and a cover 85b. This construction permits the refractorylining 96 to be rammed into place in a sidewise direction with respectto the plane of the loop channel 91 which is produced, thus insuringease of ramming, a more perfect lining, and a ready inspection of thesame. Both the bottom and cover of the shell are divided andelectrically insulated in a medial plane which is perpendicular to theplane of the loop and axially aligned with the axis of the loop.

The general features of the divided induction heating casing providingfor convenient placing of lining material are described and claimed inmy Patent No. 2,060,136, November 10, 1936. The method of ramming thelining material in such a casing is disclosed and claimed in my PatentNo. 2,008,732, July 23, 1935.

A transformer core 98 in the shape of a closed E has its central leginserted through the shell within the channel loop. A primary coil 98 isplaced upon this central leg within the opening through the shell. Thecoil is partly within the plane of the channel loop. When metal isdisposed in the loop it forms the secondary of the transformer. Theplane of the transformer core is perpendicular to the plane of thechannel loop and also perpendicular to the axis of the loop, i. e.perpendicular to the vertical plane of division of the shell 85.

The through opening of the shell is encased by a tubular shell memberI00, which is insulated from the other portions of the shell and whichis preferably composed of a non-magnetic material such as bronze. Thismember is provided with axial ribs l0! on its inner surface for morerapid and efflcient cooling by the air blast from the conduits 19 and islined on its outer surface by a strip of high melting point metal I02such as steel in the plane of the channel loop toavoid leakage of metalto the transformer coil. Any leakage through the refractory lining wouldmost likely occur in the plane of the channel loop.

Here it may be noted that the plane of the channel loop is parallel toand passes considerably below the axis of rotation Z of the furnace.This permits both legs of the loop to be filled with metalsimultaneously from the bottom upward when the furnace is tilted forthat purpose,

it being understood that the tilting is not too sudden. The arrangementis also conducive to good circulation of metal across the furnacebeneath the carbon covering so as to obtain good contact therewith. Atno time in normal operation do the planes of the channel loops dropbelow 45 degrees with the horizontal.

The loop is circular on its inner surface 91a at the side toward thefurnace. Beyond this a pocket I03 extends into the furnace through thelining thereof in a width which is equal to the greatest diameter of theoutside of the loop, which diameter lies in the plane of the transformercore. The loop on the side away from the furnace is somewhat in theshape of the letter V is rounded at 91b across the junction of the legsof the V. It does not come .to a sharp angle or point. In fact if thestraight sides were extended the junction thereof would lie whollyoutside the actual" end of the loop. This shape is much more durablethan a pointed shape would be and produces very effective circulation ofmetal.

The legs of the channel loop -are rectangular in cross section with themajor axis perpendicular to the plane of the loop. The pocket I03 whichis formed in the furnace lining at the inner side of the loop, as shownin Fig. 9, expands from rectangular to circular as it approaches theinner surface of the furnace lining. The diameter of the circle is thesame as the length of the major axis of the rectangle. This constructionalso greatly aids the circulation of the metal in that it distributesthe metal both toward the surface of the bath to react with the coveringmaterial and also to a more limited extent toward the bottom of thebath'to keep the metal there from freezing. '1

This shape also permits the lining thereabout to have maximum strengthand durability. The axis of the pocket is radial and passes through theaxis of rotation Z of the furnace. This causes the metal to beprincipally directed upward toward the surface.

No attempt is made herein to explain the mechanical, electrical or otherprimary causes of this circulation but if such an explanation is everrequired or found desirable, the right is reserved to introduce it in sofar as it is an inherent function of the construction which isdisclosed. The heating effects of the loops are such that a unit hasbeen started with frozen metal (copper). This, however, is not the usualpractice. There is no noticeable breaking of the loop circuit even whentested with delicate electrical instruments, and this in spite of thefact that in certain positions of the furnace the hydrostatic head ofmetal on the loop may become relatively small. The location of the loopsis a matter of considerable importance. They are placed low enough, asnoted, so that the column of metal is not broken by the current usedwhen the loops are in their highest normal positions. They are notplaced so low as to carry too high a head of metal; this would tend tocause metal to force its way into or through the lining. They aredirected below the axis of the hearth whereby there will be some flow ofmetal across the bot tom of thehearth to prevent freezing there. Thisalso permits emptying with minimum turning. They are arranged onopposite sides so that one set may keep,the metal molten while someorallot the other set are removed. Here again a highposition is beneficialsince the minimum turning of the hearth is required to empty the setwhich is elevated.

The location of the pouring spout is also a matter of importance. It isdesigned to obtain Cir greatest. Also when the hearth is turned for theremoval of a heating unit the spout does not go so low as to drain allof the metal. It is placed near the side of the hearth for here themovement required for pouring-a given quantity of metal is the least. Infact, it is inclined horizontally outward. It is placed in the end ofthe furnace for here it cooperates best with the associated units andthe stream of metal from the spout is caused'to strike at about the sameplace in the strainer for all pouring positions. It would be otherwiseif the spout were radial; i. e. placed in the side of the hearth; Themetal level is kept near the central horizontal plane of the hearth. Forconstant or continuous pouring this level can be closely maintained. Forinterrupted orbatch pouring it can be approximately mainiainedby pouringoften. If the metal level is thus located the change of level for thepouring of a given quantity of metal is least.

The relationship of the pouring spout and the heating units to eachother and to the body of metal and covering material carried in thefurnace chamber is such that the covering material will not be carriedinto the spout nor will surges of metal be produced in the spout. Thisis due to the fact that the zone of pronounced circulation from theheating units is not directed to-' ward the spout opening. There will,of course, be some circulation of metal throughout the entire body ofmetal just as there always is in any continuous body of fluid when adisturbance is created in any part thereof; but it is only the zone ofpronounced circulation which requires control. In the specificembodiment herein illustrated, this relationship is obvious. Forexample, it may be observed from Figs. 1 and 6 that the spout andnearest heating unit are located well away from. each other and that thespout opening is near the bottom of the main chamber and well below thecovering material; and it may be observed from Figs. 1 and '7 that theheating unit channels or chambers are directed transversely oi the axisof the main furnace chamber and open into the main chamber near thebottom and well below the material and are directed vertical planesparallel to the central axis of the zone of circulation were placed oneither side of the heating unit chamber so as to enclose it,'.

the nearestof these planes would be located well to one side of. thespout opening. In this particular embodiment the planes would be perpendicular to the longitudinal axis of the furnace.

The temperature of the bath may be controlled by a thermo-couple' it or,other suitable temperature controlling device placed in the bath nearthe pouring end and connected properly for supervision of the currentapplied to the heaterunits. The thermo-ccuple is protected by arefractory tube, the high purity of the metal in the furnace permittingof this here, whereas before it was believed to be impractical forcopper on account of the very rapid corroding effect of theoxygen-bearing metal on the refractory tube.-

When the baflle 46 is used at the intake end of the hearth and solidmetal is charged beyond aioassa metal of high quality, which provideclose and accurate temperature and refining control; and which in otherrespects constitute a distinct advance in the art "While only oneembodiment of the invention has been illustrated and described it is tobe understood that the invention is not limited to this particularembodiment but may be variously changed and have other forms within thescope of the subjoined claims.

' s I- claim:

1. An electric induction furnace comprising in combination, a horizontalcylindrical-bottomed hearth, a plurality of, induction heating unitsthereon some of which are on each side of a vertical plane through theaxis of the hearth, said heating 'units each including a secondary metalchannel loop the plane ofwhich is parallel to the axis of the hearth andnormally inclined at an angle to both vertical and horizontal planes,and a pocket in said hearth connecting the chamber thereof with thesecondary channel loop, said pocket being rectangular in section wheresaid loop enters it and spreading as it approaches the hearth chamberuntil it becomes circular in section with a diameter equalto the lengthof the major axis of the rectangular section.

2. An electric induction furnace comprising in combination, a horizontalcylindrical hearth,

mounted to turn about its longitudinal axis, and

induction heating units disposed on each side of a vertical planethrough the axis thereof, said hearth being provided with a pouringspout the inner opening of which is disposed between the inner ends ofsaid heating units, each unit having a secondary channel loop whoseplane is parallel to the axis of the hearth, the heating units beinglocated below the level of the pouring spout wherebyv those on bothsides are kept full of metal during normal pouring from the furnace, andwhereby the heating units on one side are kept full of metal when thoseon the otherside are emptied for removal or repair.

3. A furnace asset forth in claim 2 in which the heating units aredisposed at an angle to ahorizontal plane and in which the planes of theloops in normal operations never make an angle 5. A furnace as set forthin claim 2 which fur ther includes a pocket joining the loop with thePouring opening being'located: at one'side of the axis of rotation, andan induction heating unit secured exteriorly thereto, said unitincluding a secondary channel loop whose plane is parallel to the axisof the hearth.

7. An inductioh furnace comprising in combination, a hearth having alining and a retaining shell, a secondary heating loop disposed whollyoutside the hearth lining and shell, and a deep pocket extendingentirely through the lining of said hearth and connecting both legs ofthe loop in common with the chamber within said hearth, I

said pocket being nowhere smaller in cross-sectional area than thegreatest trans-planar area circumscribed by the loop and extending fromthe secondary loop for a distance which is considerably greater than thethickness of the secondary channel before it becomes greater incrosssectional area than at the loop.

8. In an electric induction furnace in combination, a hearth providedwith a metal casing, an induction heating unit therefor provided with ametal shell, said casing and shell being provided with mating attachingfaces, a support on said casing for said shell, said support extendingalongside said-shell and being provided with an attaching surfacealigned with the direction in which said shell must move to bring saidfaces together in parallel relationship, and means for attaching andinsulating said shell on said suppor 9. An induction furnace as setforth in claim 8 itially secured to and insulated from the metal.

parts of the casing or shell and to which the final attaching means areanchored, whereby the parts may have relative sliding movement duringassembly on surfaces other than the insulated surfaces.

10. An electric induction furnace as set forth in claim 8 in which saidsupporting means includes brackets, and insulated plates on saidbrackets upon which said heating unit is seated, and later slid intofinal position.

11. The method of exchanging a heating unit on a horizontal cylindricalfurnace provided with removable heating units on each side havingsecondary loops parallel with the axis of the furnace, which comprisesshutting off current from a heating unit which is to be removed from oneside while maintaining the current on a unit on the other side, turningthe furnace about its axis until the first heating unit is empty, andthen reminimum rotation of the hearth and wherebythe spout willcooperate with a simple and relatively small movement with relatedarticula I elements.

13. An electrical furnace comprising in combination, a horizontalcylindrical-bottomed hearth oscillatable about its longitudinal axis,

heating units disposed on each side of the hearth below .the centralhorizontal plane having channelsnormally directed upwardly at an angleto the vertical and horizontal planes, the angles with the horizontalplane being smaller than with the vertical plane, and a pouring spout inthe hearth arranged to pour metal in an axial direction, said spoutbeing located near the central horizontal plane of the hearth, all forthe purposes set forth.

14. An electrical furnace comprising in combination, a hearthoscillatable about a horizontal axis, upwardly inclined heating units oneither side of said axis, having channels entering the hearth below theaxis, and an axially directed pouring spout on one side of the axis andnormally at. the same elevation as the axis.

15. An electrical furnace as set forth in claim 14 in which saidinclined channels are directed toward a line which is substantiallybelow the axis of the hearth.

16. An electrical furnace as set forth in claim 14 in which saidinclined channels are directed toward a line which is substantiallybelow the axis of the hearth, and which further includes a pocket foreach channel which is flared vertically'and has its axis radial to thehearthaxis.

17. In an electrical furnace, in combination, a horizontally elongatedhearth mounted to turn about its longitudinal axis, means for chargingmetal at one end of the hearth and means for pom-ing metal at the otherend of the hearth, a battle near the charging end extending downwardfrom the roof of the hearth into the metal, and means forheating themetal in the hearth which produces an effective circulation of metal onboth sides of said baflle.

18. An electric induction furnace for molten metal, comprising incombination, a metal-holding hearth supported for tilting movement abouta horizontal axis, an induction heating unit, including a loop channelfor molten metal and induction heating means for the metal in thechannel disposed on the side of the hearth with the channelapproximately radial to the axis, and a pouring spout located at oneside of and approximately aligned with said axis.

19. An electric induction furnace for molten metal, comprising incombination, a horizontal cylindrical metal-holding hearth supported fortilting movement about its longitudinal axis, an induction heating unit,including a loop channel for molten metal and induction heating meansfor the metal in the channel disposed on the side of the hearth with thechannel approximately radial to the axis, and a pouring spout located inthe end of said hearth at one side of and approximately aligned withsaid axis.

20. Apparatus as set forth in claim 19 in which said spout in normalpouring position of the furnace is disposed approximately in a centralhorizontal plane.

21. An induction electric furnace, comprising in combination, a. hearthfor holding a bath of molten metal, means for supporting the hearth toturn about a horizontal axis, external independent induction heatingunits removably disposed on each side of the horizontal axis, and meansfor pouring metal from the hearth at a point locatedbetween the heatingunits, the hearth construction and heating unit arrangement being suchthat by tilting the furnace either of the units may be emptied while theother and a portion of the hearth is left full of metal, whereby a body.of the metal may be maintained in molten condition on one side while aunit on the other side is made accessible for replacement or repair.

22. An induction electric furnace, compri in combination, a horizontalcylindrical-bottomed of the units may be emptied while the other and t aportion of the hearth is left full of metal,

whereby a body of the metal may be maintained in molten condition on oneside while a unit on the other side is accessible for replacement orrepair.

23. A furnace as set forth in claim 22 in which each unit comprises aloop cnel outside the hearth and electric induction heating meanstherefor.

2%. In an electrical furnace, in combination, a horizontally elongatedhearth turnable about its longitudinal axis, said he having a chargingopening at one end and a pouring spout at the other end, said pouring.spout being located at one side of the axis of the iurnacefand electricinduction means for heating metal at a plurality of points along thelength of the hearth 25. An induction electric furnace, comprising incombination, a horizontal cylindrical-bottomed hearth having arefractory lining and a metal shell, and apiurality of loop-channelinductionheating units ha refractory linings and metal shells detachablysecured to the hearth shell at spaced points along its, the units beingdisposed on both of the opposite sides of a vertical plane through theaxis of the hearth, where by units onone side y be excged while those onthe other e on the metal in the molten condition.

,26. An induction electric ;.--Y. comprising in combination, a hmrth, anind ction heating unit having a loop-shaped secondary 1. el, and anelongatedp'cchet connecting the er ends of the loop channel together awith the hearth, d poclset being flared from its 3502" mum crosssectional area adjacent the loopshaped channel in a tantiy lei-dikeshape through the hearth lining to its ma cross-sectional area at theinside surface of the hearth, whereby the frictional resistance tocirculation is minimized.

2'7. An electric furnace comprising in combination, a horizontalcylindrical-bottomed hearth oscillatable about its longitudinal "axis.heating units disposed on each side of the hearth below the centralhorizontal plane having channels directed upwardly at an'angle to thevertical and horizontal planes, the angles with the horizontal planebeing smaller than with the vertical plane.

28. An electrical furnace as set forth in claim 27 in which saidinclined channels are directed toward a line which is substantiallybelow the 'axis of the hearth.

29. Anelectrical furnace as set forth in claim -27 in whichsaid inclinedchannels are directed toward a line which is substantially below theaxis of the hearth, and which further includes a pocket for each channelwhich is flared vertl- V cally-and has its axis 1' to the hearth axis.

till-An electrical furnace comprising in combination, a horizontalcylindrical bottomed hearth osciliatable about its longitudinal axis,the furnace being normally charged with metal to a level above thehorizontal axis and the metal being covered with a bed of carbon,heating units disposed on each side on the hearth below the centralhorizontal plane having channels directed arouses furnace, the angleswith the horizontal plane being smaller than with the vertical plane;whereby metal heated in the heating units is directed upward and acrossbeneath the covering of carbon.

on the metal. I

31. A furnace for producing purified copper, copper alloys or the likecomprising: a main chamber for holding a quantity of molten metal;

a a loop cber counicating with the bottom of said 'ain chamber andextending downwardly therefrom; means for heating metal in said loop "aleg chamber of relatively small cross-sectional chamber; and a pouringspout communicating with said at t. chber only adjacent the bottomthereof and well away to one side fro the vertical planes enclosing saiddownwardly extending loop-chber;

33. A furnace for producing purified copper. copper alloys or the likecomprising: a main chamber for holding a quantity of molten metal; a legchamber of relatively small cross-smtionai area counicating with thebottom of said main lawand extending downwardly therefrom;

means for heating metal in said leg cber; a "pouring spout counicatingwith said chamber only -adjacent the bottom thereof and well away to oneside from the vertical planes enclosing said downwardly-extendingleg=chamher, and independent means for heating metal in said spent.

3%. A furnace for producing ped copper, copper alloys and the like,comprising: a

chamber for holding a quantity of molten metal with a layer of coveringmaterial thereon; an

auxiliary metal holding chamber counicat ing with said main chamber nearthe lowest part of the bottom thereof and well below the normal bottomsurface ofsaid covering material, said point well beneath the normalbottom surface of said covering material and well toward the bottom ofthe main chamber, whereby to prevent floating covering material fromentering the spout, said spout opening being disposedv well awayto oneside of the zone of circulation from said auxiliary chamber, whereby toavoid circulation of metal in and the entry of ering material into saidspout.

ed cov- 35. A furnace for treating molten metal in the presence offloating material and adapted to deliver the-metal to a pouring spoutfree from surges of metal and free from floating material,

comprising in combination; a main chamber for holding a quantity'ofmolten metal, an aumliary chamber and heating means therefor, saidauxillary chamber communicating with the lower portion of said mainchamber where it will be completely submerged beneath the metal andextending downwardly from its inner communicating end whereby to producea major upwardly directed zone of active circulation of metal in themain chamber, and a pouring spout communicating only with the lowerportion of said main chamber where the communicating opening will besubmerged beneath the metal, said spout opening being located sumcientlyto one side of the major zone of circulation of metal in said mainchamber to prevent surges of metal in the main chamber or floatingmaterial from entering the spout.

DAVID L. SUMMEY.

